Highbrows with their heads in the clouds have libidos too, along with towering egos. You have only to observe the members of the fictional Fugue String Quartet as they quarrel, cheat, get even and jockey for power to sense the fragility of the chemistry that has held this elite ensemble together for 25 years.

The new films “Quartet” and “A Late Quartet” explore similar themes with very different stories about the entanglement of musicians in a cherished composition.

The upheavals that threaten them in Yaron Zilberman’s magnificently acted film “A Late Quartet” may be wildly exaggerated. But it would be shortsighted to dismiss this deeply felt, musically savvy film, set in a refined cultural precinct of Manhattan, as sudsy melodrama.

“A Late Quartet” has an important point to make about classical music. For the musicians who play it, especially intimate chamber works in which the group members have to think, feel and breathe as one, their instruments are vehicles for conveying strong emotion. Without passion, a performance, no matter how impeccable, is just a technical feat.

In concert, high-strung artists must put aside their disagreements to work toward a common goal of seamless unity. The paradoxical drives for individual self-expression and for group harmony — along with questions of who will lead and who will follow — are a profound theme that resonates, especially in this year of savage electioneering.

The film’s musical centerpiece, Beethoven’s Quartet in C sharp minor (Op. 131), is a tumultuous 40-minute string quartet whose seven movements are to be played without a pause. The ravishing version heard in the film belongs to the Brentano String Quartet, whose recording is piercingly intense. Not surprisingly, however, the actors’ simulation of these highly trained musicians is barely passable.

Otherwise, “A Late Quartet” has exceptional performances by Christopher Walken and Philip Seymour Hoffman and very good ones by Catherine Keener and Mark Ivanir. Mr. Walken’s character, Peter Mitchell, a cellist who is much older than the others, throws the group into disarray with his announcement that the coming season will be his last. After experiencing tremors during a rehearsal, he consults a doctor, who tells him he has Parkinson’s disease. Its progression can be slowed but not arrested. His response at receiving the bad news is a husky, half-whispered “wow.”

Peter is still mourning the recent death of his wife, Miriam (the mezzo-soprano Anne Sofie von Otter, who is shown singing in a flashback). Departing from his customary screen persona of eccentric hothead, Mr. Walken portrays Peter as a dignified, sorrowful peacemaker who often seems on the brink of tears.

As the quartet’s other members absorb the shock, the volatile second violinist, Robert Gelbart (Mr. Hoffman), declares that he would like to begin sharing the chair occupied by the imperious first violinist, Daniel Lerner (Mr. Ivanir). Robert’s wife, Juliette (Ms. Keener), the group’s violist, who is very close to Daniel, disparages her husband’s ambition, and her insensitively worded criticisms drive him into such a fury that he has a one-night fling with his sometime jogging partner (Liraz Charhi).

Robert barely bothers to conceal his infidelity, and when Juliette discovers his betrayal, she is struck to the quick. Nobody imbues the role of wronged wife with more disdainful loathing than Ms. Keener. She directs a deadly, expressionless gaze at Robert, who can barely control his emotions, once his demons are unleashed.

Daniel teaches violin to the Gelbarts’ attractive daughter, Alexandra (Imogen Poots), who has just begun to live on her own in Manhattan. Alexandra acts out her long-simmering rage at her parents’ neglect over the years by impulsively initiating an affair with Daniel. Ms. Poots is scary as this embittered, rebellious diva in training. Daniel’s sudden abject acquiescence to Alexandra, whom he has been shown tormenting with his disapproval, is a shock until you realize that he is even more bottled up than Robert.

The conflict between Daniel and Robert, once aired, threatens to become a philosophical war over the group’s direction, waged between a control freak and a free spirit. And the screenplay, by Mr. Zilberman and Seth Grossman, persuasively argues both sides.

“A Late Quartet” has a semiformal structure that roughly parallels that of a piece of music, covering all the emotional bases before coming to rest. With less sensitive performances, this hothouse flower of a film might have seemed stiffly programmatic. But its great acting fills in the holes and smooths over the bumps in the same way that brilliant musicianship transforms a composition from notes and phrases into something ineffable.

Directed by Yaron Zilberman; written by Seth Grossman and Mr. Zilberman, based on a story by Mr. Zilberman; director of photography, Frederick Elmes; edited by Yuval Shar; music by Angelo Badalamenti; production design by John Kasarda; costumes by Joseph G. Aulisi; produced by Vanessa Coifman, David Faigenblum, Emanuel Michael, Mandy Tagger Brockey, Tamar Sela and Mr. Zilberman; released by eOne Entertainment. Running time: 1 hour 45 minutes.